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Problem019.js
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34 lines (27 loc) · 918 Bytes
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/*
You are given the following information, but you may prefer to do some research for yourself.
* 1 Jan 1900 was a Monday.
* Thirty days has September,
April, June and November.
All the rest have thirty-one,
Saving February alone,
Which has twenty-eight, rain or shine.
And on leap years, twenty-nine.
* A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
*/
export function countingSundays () {
let n = 0
let dow = 2
const months = [31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
for (let y = 1901; y <= 2000; y++) {
months[1] = 28 + ((y % 4 === 0 && y % 100 !== 0) || y % 400 === 0)
for (const month of months) {
dow += month % 7
if (dow % 7 === 0) {
n++
}
}
}
return n
}